On high-resolution computed tomography (HRCT) scans, potentially cancerous masses appear as radio-opaque nodules. “Screening” HRCT scans are now offered commercially to target patients at high risk for lung cancer. Modem high-resolution systems are now able to identify many small, potentially cancerous lesions not previously visible in such scans. However, these lesions pose a difficult diagnostic problem; because they are small and peripherally disposed in the lung, they are difficult to reach in order to take a tissue sample. To diagnose cancer, a tissue or cellular sample at a suspect site is often acquired either by transthoracic needle aspiration or during a bronchoscopy procedure. In the bronchoscopic procedure, small forceps, a fine needle, or a cytological brush are advanced through a biopsy channel of a flexible scope and inserted into the major lobes of the affected lung to reach a suspect site that is disposed near a relatively large airway. Current bronchoscopes are only able to fit within the relative large branches of the bronchial system.
Transthoracic needle aspiration is very invasive and is typically reserved for peripheral lung nodules suspected of being cancerous. However, transthoracic needle aspiration can compromise patient health and produce infections. To minimize damage to surrounding tissue and organs, clinicians rely heavily on fluoroscopic C-arms and HRCT to guide the needle to the location of the identified suspect tissue mass. Many procedures are performed while the patient is within the CT suite to enable a biopsy needle to be inserted, steered, and continually re-imaged with a fluoroscope in incremental steps to verify its position relative to a suspected tumor. Unfortunately, transthoracic needle aspiration can compromise patient health and requires prolonged use of imaging systems that impose a substantial financial expense on the patient, and a high time cost on the hospital. Thus, bronchoscopy is a more preferred method of extracting lung tissue for biopsy purposes than is transthoracic needle aspiration.
Bronchoscopy involves the insertion of a fiber-optic bundle into the trachea and central airways in a patient's lung. Navigation of the airway relies on the clinician's ability to direct the scope head into the appropriate region. Histological biopsy samples can be obtained using forceps, a transbronchial needle aspiration, with brush cytology, or by bronchial lavage. Though still invasive, this method is much safer and is not considered to be traumatizing to the patient, in contrast to the transthoracic needle aspiration method. Despite this benefit, the large diameter of commercially available bronchoscopes restricts their entrance into small airways where nodules are commonly found, thus requiring the clinician to either steer the forceps/needle/brush blindly or use fluoroscopy to navigate to these regions throughout the lung in hopes that a representative specimen is obtained from the site actually identified as potentially cancerous.
At present, fluoroscopic C-arms are commonly used in bronchoscopy suites to assist clinicians in navigating the airways by projecting orthogonal views of the thoracic cavity in real-time. Unfortunately, drawbacks of this method are: (1) maneuvering a catheter in two separate planes is perceptually awkward; (2) images provided by a conventional bronchoscope are unclear or “fuzzy” and it is relatively difficult to see anatomical detail; (3) it is cumbersome to continually adjust the C-arm; (4) the radiation load associated with continued fluoroscopy is detrimental to the health of both the patient and the physician. Also, position coordinates of the bronchoscope cannot be measured or calculated with a fluoroscope, precluding its integration into any graphic interface and making it difficult to keep a historical record of the path followed by the bronchoscope, should such a record be needed during follow up examinations.
An ideal strategy for detection of suspect nodules in the lung would involve a minimally invasive biopsy of the potentially cancerous tissue mass, optical imaging of the epithelial layer, and real-time archiving of examination findings—without the need for expensive, radiation-based imaging systems. Ideally, it should be possible to visually guide a bronchoscope through very small airways, while maintaining a repeatable reference to the location of the bronchoscope in the airways. In addition, it would be desirable to produce data that show the paths followed and the regions of the airways that were visited during the bronchoscopy to enable a physician to easily revisit a specific nodule location at a later time, with minimal time required to retrace the branching path that must be followed to reach that location. The data recorded and stored during such a guided bronchoscopy would enable a physician to contest a charge that the physician failed to take appropriate steps to detect a malignant tissue site in the lungs, should a charge of malpractice arise.
The benefits of visually guiding a device through a lumen in a patient's body are not limited to bronchoscopes or to diagnostic studies of the lung. Clearly, it would also be desirable to guide a flexible endoscope through other body lumens, for example, through a gastric lumen so as to avoid entering the pancreatic duct in a patient when advancing an endoscopic probe beyond the pyloric valve of the stomach. A flexible endoscope might also be more efficiently advanced through the cardiovascular system of a patient if it were possible to visualize the anatomical disposition of the endoscope with reference to its location in a 3-D model of the system as determined with a position sensor. Additionally, an ultra-thin flexible endoscope and position sensor could also be used for navigating through the urethra for an image-guided biopsy of the prostate, which is not possible with conventional endoscopes. Other applications of this technology will undoubtedly be more apparent when its capabilities are fully realized by the medical profession.